A variety of different therapies can be delivered within the human body by catheter devices. Therapeutic devices such as dilatation balloons, stents, and embolic filters, and therapeutic agents such as drugs and radiation sources, may be positioned at or near the distal end of the catheter for delivery to a desired site within the body.
The prior art discloses numerous examples of intravascular catheters. Such catheters have found particular utility for procedures such as angioplasty and stent deployment. Of particular interest recently is improving catheters for use in percutaneous transluminal coronary angioplasty (PTCA) procedures. In typical PTCA procedures a guiding catheter is advanced in the patient's vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guide wire is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guide wire crosses a lesion to be dilated. A dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient's coronary artery over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with inflation fluid one or more times to a predetermined size at relatively high pressures so that the stenosis is compressed against the arterial wall and the wall expanded to open up the vascular passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter and the guidewire can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery (i.e. reformation of the arterial blockage) which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate of angioplasty alone and to strengthen the dilated area, physicians now normally implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel or to maintain its patency. Stents are usually delivered to a desired location within a coronary artery in a contracted state on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded within the patient's artery to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
With regard to coronary catheters, two main types of catheter designs, over-the-wire (OTW) and rapid-exchange (RX), dominate these applications. Each of these designs has its advantages and disadvantages. OTW catheters track over their entire length on a guidewire, which allows them to follow the wire easily and allows the direct transmission of longitudinal force over the guidewire. Additionally, these catheters allow for guidewires to be exchanged once the catheter has been advanced into position, which may be desirable when different guidewire attributes (e.g., tip curvature or radiopaque markers) are needed. However, these systems require the use of a long guidewire (e.g., 300 cm in length) and cannot be effectively operated by one person.
RX catheters typically use shorter guidewires (e.g., 180 cm in length) which allow the catheter to be operated by a single physician. The physician is able to hold the guide catheter and guidewire with one hand while using his/her other hand to advance or retract the catheter along the guidewire. However, because the entire length of the RX catheter does not slide over the guidewire, the direct transmission of longitudinal force along the path of the guidewire may be compromised, and wire exchange can not be performed once the proximal catheter guidewire port is advanced into the patient. Another problem with the design of RX catheters is that, compared to traditional OTW catheters, it results in catheters which have inferior pushability and also tend to buckle and/or kink—especially at or near the proximal (or rapid-exchange) guide wire exit port.
More recently introduced coronary catheters are hybrids of the OTW and RX catheters, sometimes referred to as “convertible” catheters. For example, U.S. Pat. Nos. 5,334,147 and 5,380,283 to Johnson teach the construction of a balloon catheter having a proximal portion that includes an aperture through the wall of the catheter into the guidewire lumen. The aperture is covered by a frangible wall (e.g., a thin-walled tube sealed to the catheter body in a position to cover the aperture portion). The frangible wall may be punctured by a guidewire, allowing the guidewire to exit the catheter guidewire lumen via the aperture. Thus, providing both rapid-exchange and over-the-wire capabilities.
U.S. Pat. No. 5,472,425 to Teirstein describes a catheter having a guidewire lumen covered by a rupturable membrane that extends along substantially the entire length of the catheter, whereby the membrane may be intentionally punctured at any desired location by the guidewire. Thus, providing both rapid-exchange and over-the-wire capabilities. The use and general construction of the catheter are related, although no materials or specific constructions for the rupturable membrane are taught.
Commonly owned and co-pending U.S. patent application Ser. No. 10/402,083, filed on Mar. 28, 2003, to Armstrong et al describes a unique convertible catheter that comprises a guidewire lumen having a thin covering that is easily punctured to form a guidewire exit port at virtually any desired point along the catheter. The thin covering may be integral with the catheter shaft, or may be a separate component that covers only the portion of the catheter shaft immediately adjacent the outer portion of the guidewire lumen, or may be a thin tubular construct that surrounds the entire catheter shaft. In one disclosed embodiment the thin covering is made from a thin tape of porous expanded polytetrafluoroethylene (ePTFE) helically wrapped about the exterior of a catheter shaft. The wrapping can be accomplished, for example, in two opposing directions parallel to the length of the catheter shaft, resulting in a bias-ply construction. This thin covering offers good transparency and is easily punctured (e.g., by the end of a guidewire) and yet is resistant to tearing at the puncture site. Other disclosed materials for the thin covering include, for example, polyethylene terephthalate (PET), polyethylene, polypropylene, polyamide, etc. Porous polymers, optionally provided with a thin, non-porous coating, may be advantageously used because of their excellent flexibility. Most preferred are tapes made from thin ePTFE film that has been provided with a porous or non-porous coating of a thermoplastic such as a thermoplastic fluoropolymer, preferably fluorinated ethylene propylene (FEP). Exemplary ePTFE films can be made as taught by U.S. Pat. Nos. 3,953,566 and 4,187,390 to Gore. More preferred are ePTFE films made as taught be U.S. Pat. No. 5,476,589 to Bacino. The construction of thin, helically-wrapped tubes from ePTFE films and thermoplastic-coated ePTFE films, and the method of providing the coating onto the ePTFE films, are taught, for example, by U.S. Pat. No. 6,159,565 to Campbell et al. The guidewire lumen can be in the form of a slot made into the catheter shaft, with the slot provided with the thin covering. Preferably, the slot extends for most or even all of the length of the catheter. The slot can be covered with a thin tubular covering that coaxially encloses the entire catheter shaft or alternatively a strip of thin tape-like covering material that covers the slot and is adhered to the surface of the catheter shaft immediately adjacent both sides of the slot. A multiplicity of pre-formed openings may be provided through the thin covering if desired. Also, the slot covering material may take the form of a braid or winding of filaments. This braid or winding of filaments may optionally be covered with a thin polymeric tube except for the filaments immediately over the top of the slot which preferably remain exposed and allow for passage of the end of a guidewire through any interstice between adjacent filaments.
A further problem with conventional balloon catheters for intravascular procedures, such as angioplasty and stent delivery, is such catheters frequently have stiff proximal sections to facilitate advancement of the catheter within the patient's body lumen and relatively flexible distal shaft sections to facilitate passage through tortuous anatomy such as distal coronary and neurological arteries without damage to the luminal wall. Typically, there is an intermediate shaft section or junction between the relatively stiff proximal shaft section and the relatively flexible distal shaft section that provides a transition between the proximal shaft section and the distal shaft section.
A variety of proposed solutions to the problems of providing catheters with rapid-exchange capabilities, good pushability, smooth flexibility transition from proximal end to distal end, and good resistance to buckling and/or kinking (especially at the proximal (or rapid-exchange) guide wire exit port) have been attempted. However, the search continues for a catheter that overcomes all of these problems.